Oxidative stress and chronic inflammation are crucial in the pathogenesis of thyroid diseases. Thyroid peroxidase (TPO) is essential for thyroid hormone synthesis, and its activity can be influenced by phenolic compounds. Bioactive food components impact redox homeostasis, regulate pro-inflammatory enzymes and affect MAO activity, potentially alleviating metabolic and mood disorders often associated with thyroid dysfunction. These factors are particularly relevant in metabolic syndrome, where thyroid dysfunction can exacerbate the condition. Given the sometimes conflicting dietary recommendations, understanding these mechanisms may help clarify the impact of nutrition on thyroid health and guide more effective nutritional strategies.